1. Field of the Invention
This invention relates to a method of and an apparatus for recording and erasing using a film which allows repeated recording and erasing (a rewritable recording film), and to such a rewritable recording film.
2. Description of the Related Art
Because of their relatively simple construction, recording means like thermal recording apparatus or thermal transfer recording apparatus, in which a thermal head or the like is used to record image information on a recording medium such as paper, are being widely used as recording units in various apparatus including printers and facsimile apparatus.
As an example of such recording means, a recording unit for a facsimile apparatus using a thermal recording sheet will be described. The recording unit basically operates as follows: First, when a recording signal is supplied to the recording unit of the facsimile apparatus, heating elements of the thermal head are selectively energized to generate heat with a predetermined timing in accordance with this recording signal, thereby developing color at desired positions on the thermal recording sheet so as to form an image thereon.
With such a conventional recording unit in a facsimile apparatus or the like, an image once formed on a thermal recording sheet by developing color thereon cannot be erased. Therefore, it is impossible to form a different desired image on the same recording sheet.
As a result, the operating cost of such units is high. Particularly in the case of low-priced and economical facsimile units, for example, for the home, it is necessary to keep costs down to a minimum.
In view of this, rewritable recording films allowing repeated recording and erasion have recently been developed with a view to reducing operating costs or to improving a man-machine interface for balance inscription on a prepaid card or the like. Examples of such rewritable recording films include the resin type or the organic low-molecular-weight-material-type films (hereinafter referred to as "the cloudy-type" films) disclosed in Japanese Patent Laid-Open No. 55-154198, 57-82086, 02-117891, etc, and those disclosed in WO 90/11898, Japanese Patent Laid-Open No. 02-188294, etc.
Being constructed as described above, the conventional recording/display apparatuses are not capable of recording an image on a recording medium on which some other image has already been recorded, which means a large amount of recording medium must inevitably be used. Further, for a rewritable recording medium to be re-used, perfect erasability is indispensable for practical use, and there has been no method or apparatus for recording and erasing or a rewritable recording film available which satisfies this condition.
To discuss the point in more detail, there is the problem that a perfect erasure cannot be attained even in a case where a desired image is formed selectively with a first kind of heat energy and entirely erased with a second kind of heat energy. Specifically, in the case, for example, of a reflection-type cloudy film, in which a metal reflective layer of aluminum or the like is provided under the recording layer that is formed of a resin/organic-low-molecular-weight material, those portions on the film where selective recording had been effected can be visually perceived as such even after they have been erased, which means a perfect erasure has not been achieved. It may be assumed that this is attributable to the fact that those film portions where erasure has been effected subsequent to recording are different from those where erasure has been effected with no previous recording in terms of the transparency and reflecting condition of the recording layer. Further, in the case of a dye-type film, it may also be assumed that a perfect erasure is made impossible by the difference between those film portions where erasure has been effected subsequent to recording and those where it has been effected with no previous recording in terms of the erasing condition of the recording layer.
Further, notwithstanding the fact that an exact positional control must be performed during the recording/erasing operation, if a perfect erasure is to be achieved, no such positional control has conventionally been performed. The prior-art techniques, have thus remained short of perfection in erasing.
In addition, in the case where the same thermal head as is used for recording is used as the heating means for erasing the presence of small gaps between the heating elements will allow some film portions to remain unerased.